diff --git a/src/lib/netlist/nl_setup.cpp b/src/lib/netlist/nl_setup.cpp
index a3a49513a9f..c48ca48ae0c 100644
--- a/src/lib/netlist/nl_setup.cpp
+++ b/src/lib/netlist/nl_setup.cpp
@@ -100,7 +100,7 @@ void setup_t::register_model(const pstring &model_in)
 	if (pos == model_in.end())
 		log().fatal(MF_1_UNABLE_TO_PARSE_MODEL_1, model_in);
 	pstring model = model_in.left(pos).trim().ucase();
-	pstring def = model_in.substr(pos + 1).trim();
+	pstring def = model_in.substr(std::next(pos, 1)).trim();
 	if (!m_models.insert({model, def}).second)
 		log().fatal(MF_1_MODEL_ALREADY_EXISTS_1, model_in);
 }
@@ -818,11 +818,11 @@ void setup_t::model_parse(const pstring &model_in, detail::model_map_t &map)
 			log().fatal(MF_1_MODEL_NOT_FOUND, model_in);
 	}
 
-	pstring remainder=model.substr(pos+1).trim();
+	pstring remainder=model.substr(std::next(pos, 1)).trim();
 	if (!remainder.endsWith(")"))
 		log().fatal(MF_1_MODEL_ERROR_1, model);
 	// FIMXE: Not optimal
-	remainder = remainder.left(remainder.begin() + (remainder.len() - 1));
+	remainder = remainder.left(std::next(remainder.begin(), (remainder.len() - 1)));
 
 	std::vector<pstring> pairs(plib::psplit(remainder," ", true));
 	for (pstring &pe : pairs)
@@ -830,7 +830,7 @@ void setup_t::model_parse(const pstring &model_in, detail::model_map_t &map)
 		auto pose = pe.find("=");
 		if (pose == pe.end())
 			log().fatal(MF_1_MODEL_ERROR_ON_PAIR_1, model);
-		map[pe.left(pose).ucase()] = pe.substr(pose+1);
+		map[pe.left(pose).ucase()] = pe.substr(std::next(pose, 1));
 	}
 }
 
@@ -854,7 +854,7 @@ nl_double setup_t::model_value(detail::model_map_t &map, const pstring &entity)
 	pstring tmp = model_value_str(map, entity);
 
 	nl_double factor = NL_FCONST(1.0);
-	auto p = tmp.begin() + (tmp.len() - 1);
+	auto p = std::next(tmp.begin(), (tmp.len() - 1));
 	switch (*p)
 	{
 		case 'M': factor = 1e6; break;
@@ -870,7 +870,7 @@ nl_double setup_t::model_value(detail::model_map_t &map, const pstring &entity)
 			log().fatal(MF_1_UNKNOWN_NUMBER_FACTOR_IN_1, entity);
 	}
 	if (factor != NL_FCONST(1.0))
-		tmp = tmp.left(tmp.begin() + (tmp.len() - 1));
+		tmp = tmp.left(std::next(tmp.begin(), (tmp.len() - 1)));
 	return tmp.as_double() * factor;
 }
 
@@ -976,7 +976,7 @@ void setup_t::register_define(pstring defstr)
 {
 	auto p = defstr.find("=");
 	if (p != defstr.end())
-		register_define(defstr.left(p), defstr.substr(p+1));
+		register_define(defstr.left(p), defstr.substr(std::next(p, 1)));
 	else
 		register_define(defstr, "1");
 }
diff --git a/src/lib/netlist/plib/pfunction.cpp b/src/lib/netlist/plib/pfunction.cpp
index 0f48860d15b..7113a6e07fb 100644
--- a/src/lib/netlist/plib/pfunction.cpp
+++ b/src/lib/netlist/plib/pfunction.cpp
@@ -86,7 +86,7 @@ static int get_prio(pstring v)
 {
 	if (v == "(" || v == ")")
 		return 1;
-	else if (v.left(v.begin()+1) >= "a" && v.left(v.begin()+1) <= "z")
+	else if (v.left(std::next(v.begin(),1)) >= "a" && v.left(std::next(v.begin(),1)) <= "z")
 		return 0;
 	else if (v == "*" || v == "/")
 		return 20;
diff --git a/src/lib/netlist/plib/poptions.cpp b/src/lib/netlist/plib/poptions.cpp
index 9defcf84975..698c813129c 100644
--- a/src/lib/netlist/plib/poptions.cpp
+++ b/src/lib/netlist/plib/poptions.cpp
@@ -133,8 +133,8 @@ namespace plib {
 			}
 			else if (arg.startsWith("-"))
 			{
-				auto p = arg.begin() + 1;
-				opt = getopt_short(arg.substr(p,p + 1));
+				auto p = std::next(arg.begin(), 1);
+				opt = getopt_short(arg.substr(p, std::next(p, 1)));
 				++p;
 				if (p != arg.end())
 				{
@@ -226,7 +226,7 @@ namespace plib {
 							{
 								line += v + "|";
 							}
-							line = line.left(line.begin() + (line.len() - 1));
+							line = line.left(std::next(line.begin(), (line.len() - 1)));
 						}
 						else
 							line += "Value";
diff --git a/src/lib/netlist/plib/pstring.cpp b/src/lib/netlist/plib/pstring.cpp
index 5396f333358..90dc1f82f1d 100644
--- a/src/lib/netlist/plib/pstring.cpp
+++ b/src/lib/netlist/plib/pstring.cpp
@@ -104,7 +104,7 @@ void pstring_t<F>::pcopy(const mem_t *from, std::size_t size)
 }
 
 template<typename F>
-const pstring_t<F> pstring_t<F>::substr(const iterator &start, const iterator &end) const
+const pstring_t<F> pstring_t<F>::substr(const const_iterator &start, const const_iterator &end) const
 {
 	pstring_t ret;
 	//FIXME: throw ?
@@ -116,7 +116,7 @@ template<typename F>
 const pstring_t<F> pstring_t<F>::ucase() const
 {
 	pstring_t ret = "";
-	for (auto c : *this)
+	for (code_t c : *this)
 		if (c >= 'a' && c <= 'z')
 			ret += (c - 'a' + 'A');
 		else
@@ -125,12 +125,12 @@ const pstring_t<F> pstring_t<F>::ucase() const
 }
 
 template<typename F>
-typename pstring_t<F>::iterator pstring_t<F>::find_first_not_of(const pstring_t &no) const
+typename pstring_t<F>::const_iterator pstring_t<F>::find_first_not_of(const pstring_t &no) const
 {
 	for (auto it = begin(); it != end(); ++it)
 	{
 		bool f = true;
-		for (auto const jt : no)
+		for (code_t const jt : no)
 		{
 			if (*it == jt)
 			{
@@ -145,14 +145,14 @@ typename pstring_t<F>::iterator pstring_t<F>::find_first_not_of(const pstring_t
 }
 
 template<typename F>
-typename pstring_t<F>::iterator pstring_t<F>::find_last_not_of(const pstring_t &no) const
+typename pstring_t<F>::const_iterator pstring_t<F>::find_last_not_of(const pstring_t &no) const
 {
-	/* FIXME: reverse iterator */
-	iterator last_found = end();
+	/* FIXME: reverse const_iterator */
+	const_iterator last_found = end();
 	for (auto it = begin(); it != end(); ++it)
 	{
 		bool f = true;
-		for (auto const jt : no)
+		for (code_t const jt : no)
 		{
 			if (*it == jt)
 			{
@@ -167,11 +167,11 @@ typename pstring_t<F>::iterator pstring_t<F>::find_last_not_of(const pstring_t &
 }
 
 template<typename F>
-typename pstring_t<F>::iterator pstring_t<F>::find(const pstring_t &search, iterator start) const
+typename pstring_t<F>::const_iterator pstring_t<F>::find(const pstring_t &search, const_iterator start) const
 {
 	for (; start != end(); ++start)
 	{
-		iterator itc(start);
+		const_iterator itc(start);
 		auto cmp = search.begin();
 		while (itc != end() && cmp != search.end() && *itc == *cmp)
 		{
@@ -185,7 +185,7 @@ typename pstring_t<F>::iterator pstring_t<F>::find(const pstring_t &search, iter
 }
 
 template<typename F>
-typename pstring_t<F>::iterator pstring_t<F>::find(const code_t search, iterator start) const
+typename pstring_t<F>::const_iterator pstring_t<F>::find(const code_t search, const_iterator start) const
 {
 	mem_t buf[traits::MAXCODELEN+1] = { 0 };
 	traits::encode(search, buf);
@@ -205,7 +205,7 @@ pstring_t<F> pstring_t<F>::replace(const pstring_t &search, const pstring_t &rep
 	{
 		ret += substr(last_s, s);
 		ret += replace;
-		last_s = s + slen;
+		last_s = std::next(s, slen);
 		s = find(search, last_s);
 	}
 	ret += substr(last_s, end());
@@ -225,7 +225,7 @@ const pstring_t<F> pstring_t<F>::rtrim(const pstring_t &ws) const
 	if (f==end())
 		return pstring_t("");
 	else
-		return substr(begin(), f + 1);
+		return substr(begin(), std::next(f, 1));
 }
 
 template<typename F>
diff --git a/src/lib/netlist/plib/pstring.h b/src/lib/netlist/plib/pstring.h
index 394b8c193de..7bb037b42cd 100644
--- a/src/lib/netlist/plib/pstring.h
+++ b/src/lib/netlist/plib/pstring.h
@@ -82,25 +82,57 @@ public:
 	// assignment operators
 	pstring_t &operator=(const pstring_t &string) { pcopy(string); return *this; }
 
-	struct iterator final : public std::iterator<std::forward_iterator_tag, mem_t>
+	class const_iterator final
 	{
-		const mem_t * p;
 	public:
-		explicit constexpr iterator(const mem_t *x) noexcept : p(x) {}
-		iterator(const iterator &rhs) noexcept = default;
-		iterator(iterator &&rhs) noexcept { p = rhs.p; }
-		iterator &operator=(const iterator &it) { p = it.p; return *this; }
-		iterator& operator++() noexcept { p += traits::codelen(p); return *this; }
-		iterator operator++(int) noexcept { iterator tmp(*this); operator++(); return tmp; }
-		bool operator==(const iterator& rhs) noexcept { return p==rhs.p; }
-		bool operator!=(const iterator& rhs) noexcept { return p!=rhs.p; }
-		const code_t operator*() noexcept { return traits::code(p); }
-		iterator& operator+=(size_type count) { while (count>0) { --count; ++(*this); } return *this; }
-		friend iterator operator+(iterator lhs, const size_type &rhs) { return (lhs += rhs); }
+		class value_type final
+		{
+		public:
+			value_type() = delete;
+			value_type(const value_type &) = delete;
+			value_type(value_type &&) = delete;
+			value_type &operator=(const value_type &) = delete;
+			value_type &operator=(value_type &&) = delete;
+			operator code_t() const noexcept { return traits::code(&m); }
+		private:
+			const mem_t m;
+		};
+
+		typedef value_type const *pointer;
+		typedef value_type const &reference;
+		typedef std::ptrdiff_t difference_type;
+		typedef std::forward_iterator_tag iterator_category;
+
+		const_iterator() noexcept : p(nullptr) { }
+		explicit constexpr const_iterator(const mem_t *x) noexcept : p(x) { }
+		const_iterator(const const_iterator &rhs) noexcept = default;
+		const_iterator(const_iterator &&rhs) noexcept = default;
+		const_iterator &operator=(const const_iterator &rhs) noexcept = default;
+		const_iterator &operator=(const_iterator &&rhs) noexcept = default;
+
+		const_iterator& operator++() noexcept { p += traits::codelen(p); return *this; }
+		const_iterator operator++(int) noexcept { const_iterator tmp(*this); operator++(); return tmp; }
+
+		bool operator==(const const_iterator& rhs) const noexcept { return p == rhs.p; }
+		bool operator!=(const const_iterator& rhs) const noexcept { return p != rhs.p; }
+
+		reference operator*() const noexcept { return *reinterpret_cast<pointer>(p); }
+		pointer operator->() const noexcept { return reinterpret_cast<pointer>(p); }
+
+	private:
+		template <typename G> friend struct pstring_t;
+		const mem_t * p;
 	};
 
-	iterator begin() const { return iterator(m_ptr->str()); }
-	iterator end() const { return iterator(m_ptr->str() + blen()); }
+	// no non-const const_iterator for now
+	typedef const_iterator iterator;
+
+	iterator begin() { return iterator(m_ptr->str()); }
+	iterator end() { return iterator(m_ptr->str() + blen()); }
+	const_iterator begin() const { return const_iterator(m_ptr->str()); }
+	const_iterator end() const { return const_iterator(m_ptr->str() + blen()); }
+	const_iterator cbegin() const { return const_iterator(m_ptr->str()); }
+	const_iterator cend() const { return const_iterator(m_ptr->str() + blen()); }
 
 	// C string conversion helpers
 	const mem_t *c_str() const { return m_ptr->str(); }
@@ -141,20 +173,20 @@ public:
 	pstring_t& operator+=(const code_t c) { mem_t buf[traits::MAXCODELEN+1] = { 0 }; traits::encode(c, buf); pcat(buf); return *this; }
 	friend pstring_t operator+(const pstring_t &lhs, const code_t rhs) { return pstring_t(lhs) += rhs; }
 
-	iterator find(const pstring_t &search, iterator start) const;
-	iterator find(const pstring_t &search) const { return find(search, begin()); }
-	iterator find(const code_t search, iterator start) const;
-	iterator find(const code_t search) const { return find(search, begin()); }
+	const_iterator find(const pstring_t &search, const_iterator start) const;
+	const_iterator find(const pstring_t &search) const { return find(search, begin()); }
+	const_iterator find(const code_t search, const_iterator start) const;
+	const_iterator find(const code_t search) const { return find(search, begin()); }
 
-	const pstring_t substr(const iterator &start, const iterator &end) const ;
-	const pstring_t substr(const iterator &start) const { return substr(start, end()); }
-	const pstring_t substr(size_type start) const { return (start >= len()) ? pstring_t("") : substr(begin() + start, end()); }
+	const pstring_t substr(const const_iterator &start, const const_iterator &end) const;
+	const pstring_t substr(const const_iterator &start) const { return substr(start, end()); }
+	const pstring_t substr(size_type start) const { return (start >= len()) ? pstring_t("") : substr(std::next(begin(), start), end()); }
 
-	const pstring_t left(iterator leftof) const { return substr(begin(), leftof); }
-	const pstring_t right(iterator pos) const  { return substr(pos, end()); }
+	const pstring_t left(const_iterator leftof) const { return substr(begin(), leftof); }
+	const pstring_t right(const_iterator pos) const  { return substr(pos, end()); }
 
-	iterator find_first_not_of(const pstring_t &no) const;
-	iterator find_last_not_of(const pstring_t &no) const;
+	const_iterator find_first_not_of(const pstring_t &no) const;
+	const_iterator find_last_not_of(const pstring_t &no) const;
 
 	const pstring_t ltrim(const pstring_t &ws = pstring_t(" \t\n\r")) const;
 	const pstring_t rtrim(const pstring_t &ws = pstring_t(" \t\n\r")) const;
diff --git a/src/lib/netlist/plib/putil.cpp b/src/lib/netlist/plib/putil.cpp
index 0f09f512242..234b4e6cbaa 100644
--- a/src/lib/netlist/plib/putil.cpp
+++ b/src/lib/netlist/plib/putil.cpp
@@ -52,7 +52,7 @@ namespace plib
 			pstring t = str.substr(p, pn);
 			if (!ignore_empty || t.len() != 0)
 				ret.push_back(t);
-			p = pn + onstr.len();
+			p = std::next(pn, onstr.len());
 			pn = str.find(onstr, p);
 		}
 		if (p != str.end())
diff --git a/src/lib/netlist/prg/nltool.cpp b/src/lib/netlist/prg/nltool.cpp
index e797399b9a1..ba0526b5408 100644
--- a/src/lib/netlist/prg/nltool.cpp
+++ b/src/lib/netlist/prg/nltool.cpp
@@ -421,7 +421,7 @@ void tool_app_t::mac_out(const pstring &s, const bool cont)
 	if (cont)
 	{
 		unsigned adj = 0;
-		for (auto x : s)
+		for (auto &x : s)
 			adj += (x == '\t' ? 3 : 0);
 		pout("{1}\\\n", s.rpad(" ", RIGHT-1-adj));
 	}
diff --git a/src/lib/netlist/tools/nl_convert.cpp b/src/lib/netlist/tools/nl_convert.cpp
index 305dcf4853d..9589794e696 100644
--- a/src/lib/netlist/tools/nl_convert.cpp
+++ b/src/lib/netlist/tools/nl_convert.cpp
@@ -318,7 +318,7 @@ void nl_convert_spice_t::process_line(const pstring &line)
 				{
 					if (m[1].len() != 4)
 						fprintf(stderr, "error with model desc %s\n", model.c_str());
-					pins = m[1].left(m[1].begin() + 3);
+					pins = m[1].left(std::next(m[1].begin(), 3));
 				}
 				add_device("QBJT_EB", tt[0], m[0]);
 				add_term(tt[1], tt[0] + "." + pins.code_at(0));